1. Field
The present disclosure relates to an apparatus and technique for a wireless communications receiver architecture and, more particularly, to an apparatus and technique for an analog adaptive receiver architecture.
2. Background Information
Typically, wireless signals are subject to interference. This interference may come from many different sources, such as, multiple-access interference (MAI) that may originate in the wireless network, other wideband interference, for example, signals from a similar wireless network using the same frequency band, or narrowband interference, for example, signals from a dissimilar wireless network using the same frequency band. These interfering signals may have a greater received power than the typical additive white noise and may be a principal source of error. In addition, a time-variant multi-path channel, or frequency band, generates detrimental inter-symbol interference and time-variant fading in a received signal. Both the multi-access interference and multipath fading may limit the performance of a wireless multi-access system. Traditionally, techniques for addressing these issues for UWB communications include a digital differential phase shift key (DPSK) demodulation or the use of a RAKE receiver.
FIG. 1 is a block diagram illustrating a traditional DPSK receiver 100 that utilizes a least-means squared (LMS) filter. The traditional DPSK receiver may include an antenna 105, a bandpass filter 110, a low-noise amplifier 120, an analog-to-digital converter 130 and a LMS filter 140. The conventional implementation of a least-means squared (LMS) filter requires storage components 150, if the observation window size in the filter is greater than one symbol duration. The delayed signals are assigned weights 160 and summed 170 before being sent to the PSK symbol detector 199. Conventionally, the PSK symbol detector extracts information from the received and filtered signals. Often, however, the DPSK receiver does not allows the UWB signal to be sampled at the Nyquist rate at a low cost. Alternatively, the DPSK receiver may use a delay spread, or observation window, for the UWB channel of less than a one symbol duration. Also, a DPSK receiver is subject to intersymbol interference (ISI) and noise amplification.
FIG. 2 is a block diagram illustrating a traditional RAKE filter receiver 200. The traditional RAKE filter receiver may include an antenna 105, a bandpass filter 110, a low-noise amplifier 120, and a PSK symbol detector 199. The RAKE filter 230 consists of multiple correlators or matched filters 242 & 248, in which the received signal is multiplied by time-shifted versions of a locally generated code sequence. The local reference signal may be stored within the matched filters 242 & 248. The module 270 often provides timing when the switches should open and close. Module 270 may also provide channel information, such as, for example, channel gains on each path to the combining module. The RAKE filter often separates signals such that each finger only processes signals received via a single (resolvable) path. A conventional RAKE filter employs a combining module 280, such as, for example, a maximum ratio combiner or equal gain combiner, to combine the signal energy distributed in the paths. Like the DPSK receiver of FIG. 1, the combining module 280, of FIG. 2, is often subject to intersymbol interference (ISI) and multiple-access interference (MAI).